1. Beta-decay studies of neutron-rich Fe, Co and Ni isotopes at LISOL using the MINIBALL detector Dieter Pauwels, Oleg V. Ivanov, Maria Sawicka, Mark Huyse, Piet Van Duppen, Thomas E. Cocolios, Yuri Kudryavtsev, Johnny Gentens, Paul Van den Bergh, Irina Stefanescu, Jarno Van de Walle, and MINIBALL Collaboration Katholieke Universiteit Leuven, Instituut voor Kern- & Stralingsfysica

2. 68 Cu 69 Cu 70 Cu 67 Ni 68 Ni 69 Ni 66 Co 67 Co 68 Co Z=28  +1  -1 +1 N=40 65 Fe 66 Fe 67 Fe 68 Fe To probe N=40 subshell gap we can look for levels interpreted as particle(hole)   68 Ni Almost nothing is known about nuclear structure of 65,66,67,68 Co ??? Nuclear Structure around semi-doubly magic 68 Ni S. Franchoo Ph.D. Thesis, Leuven 1999  p 1/2 p 1/2 -1  p 3/2 p 1/2 -1 68 Ni  (    ) 01+ 8421+ 842+2+ J.Van Roosbroeck, Phys.Rev.C 69 2004  p 1/2  p 3/2 68 Ni  (   ) 03/2- 11101/2-  f 5/2 12145/2-  g 9/2 25539/2+ J.Van Roosbroeck, Phys.Rev.C 69 2004  p 3/2 p 1/2  (  g 9/2 )   p 3/2 g 9/2 68 Ni  (    ) 06- 2421+1+  f 5/2 g 9/2 3692-  g 9/2 g 9/2 19801+ L. Weissman, Phys.Rev.C 59 1999 f 5/2  p 1/2  68 Ni   01/2- 6945/2- g 9/2 ( p 1/2 )  10079/2+ W.F. Mueller, Phys.Rev.Lett. 83, 1999 g 9/2 68 Ni   09/2+ p 1/2  ( g 9/2 )  3211/2- f 5/2  ( g 9/2 )  9155/2- p 3/2  ( g 9/2 )  14003/2- 65 Co

3. Experimental set-up Gas Cell Buffer Gas Cyclotron 30 MeV Proton Beam 238 U Targets (10 mg/cm 2 ) Mass Separator Ion Guide (SPIG)  Detection Set-up Leuven Isotope Separator-On-Line Data-acquisition System XIA DGF-4C IGOR Laser-ionized reaction products Lasers A A*A* A + + e -

4. 3 Plastic  E  -detectors Detection set-up 6-fold segmented MINIBALL Clusters Beam

5. Analysis of  -gated  events (data 2005) 67Fe 189 keV 67Co 694 keV 67Fe 1251 keV 67Fe 2054 keV 67Fe 2080 keV 67Fe 2087 keV Lasers ON FeLasers OFF

6. 67 Fe decay scheme after  analysis 67 Ni 694 313 2155 67 Co -- (1/2-) (5/2-) (9/2+) (5/2-) T 1/2 =425(20) ms 67 Co 2054 20802087 189 1251 572 67 Fe -- 1251 T 1/2 =411(32) ms Lasers on Co L. Weissman et al. PRC59 (1999) 2004

7. Single  spectrum: welcome 491 keV! (data 2005) 491 keV 694 keV Lasers ON Fe Lasers OFF COMPLETE ANSWER:  -  -  CORRELATIONS Similar half-lives No  coincidences No  coincidences

8. Cycle structure LISOL and Correlations (data 2006) Activity@tape t … Beam ONBeam OFF 1 macro-cycle …… t trig 0200 t (ms) -200 67 Fe -- 189 694 -- 67 Co 67 Ni 491 ?

9. Result: single  ’s before (-200 – 0 ms) a  -694 keV trigger 491 keV511 keV 694 keV Correlated events Random events Random subtracted Correlations Control random events!

10. Random substracted results (I) 491 keV events coming before  -694 keV 491 keV in 67 Co! 491 keV events coming after  -189 keV 491 keV after  -189 keV! 67 Fe -- 189 694 -- 67 Co 67 Ni 491 ? 329 (28) ms 67 Fe -- 189 694 -- 67 Co 67 Ni 491 T 1/2 : 329 (28) ms T 1/2 : 483 (56) ms 425 (20) ms PRC 59 2004 483 (56) ms 512 (43) ms 499 (24) ms

11. Random substracted results (II) Placing isomer T 1/2 isomeric and ground state from direct correlations 491 67 Co 0.98 (5) Branching ratios (preliminary) Grand-daughter correlations!!! 491 67 Co 189 0.95 (15) 0.05 (15)

12. Speculative interpretation -- 189 694 -- 491 411 (32) ms 499 (24) ms 20 28 1d 5/2 2s 1/2 1d 3/2 1f 7/2 1f 5/2 2p 3/2 2p 1/2 50 1g 9/2 205420802087 7/2 -  -1 [321]1/2 - ?? [440]1/2 + ?? [321]1/2 - [303]7/2 - 329 (28) ms 50%

13. Conclusions and outlook 67 Co level scheme fully analyzed Isomerism in 67 Co Isomer @ 491 keV and g.s. 67 Co fully characterized thanks to  correlations Placement, T 1/2, Branching Correlations in seconds domain thanks to Pure beams from laser ionization Read-out on a event-on-event basis Segmentation of MINIBALL clusters: Multiplicity 1 491 keV  events need for SM calculations with 48 Ca core: Allow for proton excitations across the Z=28 gap Interpretation of the isomer New beam time @ LISOL is granted for a 64-66 Fe  -decay campaign in July 2007: onset of deformation?

14. Limitations correlations Simulation

15. Random subtracted results 491 keV events coming before  -694 keV 694 keV events coming before  -694 keV No correlation!Correlation!

16. Randoms: strategy Step 2: Scan the trigger distribution in steps of 5 ms to know the number of triggers N tr. Step 3: Build the random (  -)  ’s from the dataset and normalize to N tr. t cycle 200 Step 1: A dataset of single ,  and  -  histograms H i in steps of 5 ms. t corr =N tr *5 ms t random =  t meas /t cycle *5 ms t trig 5 ms 0 t corr (ms)

17. Neutron-induced events during the proton beam ON! Neutron-induced background (data 2006) Macro-cycle: 10s/0s/1Micro-cycle: 100ms/100ms Single  events during and 15 ms after proton beam ON are rejected. 85 ms 115 ms

18. Result: e.g. single  ’s before (-200 – 0 ms) or after (0 - 200 ms) a  -694 keV trigger 491 keV 511 keV 694 keV 67 Fe -- 189 694 -- 67 Co 67 Ni 491 ? In 67 Co!! BEFORE AFTER Count-rate  ’s: ~35 Hz # triggers:6353  T/histogram/trigger:85 ms # randoms/histogram: ~19000

19. Z=28  +1  -1 +1 N=40 70 Co 69 Co 68 Co 67 Co 66 Co 65 Co 71 Ni 70 Ni 69 Ni 68 Ni 67 Ni 66 Ni 72 Cu 71 Cu 70 Cu 69 Cu 68 Cu 67 Cu 69 Fe 68 Fe 67 Fe 66 Fe 65 Fe 64 Fe 28 40 1f 7/2 2p 3/2 1f 5/2 2p 1/ 2 1g 9/2  50 40 E 28 N Z 67 Fe situated on the chart of nuclides Experiments: 1. Nov. 2005 2. June 2006